Manufacture of magnetic cores



-f .zaj: manuracrnas or men Adolph i Bandur," Ber-Wyn, 111., asaignor" to Western Electric Company. Incorporated, New

York, N. Y'.;, a corporationoi York unwise. Application mast, 0,1940, Serial No. 312,686 v 3 -jimproved methods for producing insulated dust i -typemagnetic cores having substantial mechan- 0- ical strength and magnetic properties established within desired limits.- r

In the manufacture of insulated dust mag-- netic-cores it is customary to puli'lerize a magynetic metal or alloy into small particles, coat the particles with-a combination insulation and j-bi'nden-and then form the coated particles into a bodyathigh pressure; Cores of this type are' 'used in fa variety of apparatus and different core properties are required for different fields oi service.v The effective permeability of, the core is nearly always important and in many instances -it'.is desirable to produce cores having an eiiec- I tive permeability rating established accurately within-predeterminedand narrow limits. effective, permeability of these cores is influenced The by the spacing oi the particles, 'otherfactors being equal, and in some cases the'permeability can. be regulated by incorporatinga particle able for this purpose.

spacing'agent or filler in the core. These fillers should be chemically inert,- non-metallic and nonmagnetic.

Kaolin and eou'o dar'nay' are: generally sa These materials canbe incorporated in the core by dry mixing them with thecoated particles and then pressing the 'mixture in the usual manner. provided that the I magnetic particles are. relatively coarse and that theproportion .or' filler is small. However, this procedure is not suitable when very small'magnetic particles, such as 300 or 400 mesh or smaller, or a large proportion of filler are used for the cores. Under either of these conditions a .dry

mixture of particles and kaolin or colloidal clay is very' flufl'y and diiilcult to handle without the loss of some of the filler material and consequent disruption of the proper ingredient proportion balance. When attempts are made to press the dry mixture in a die cavity, the fluffy material tends to blow past the forming member before any compactingis accomplished. Also. the spacing material tends to segregate, with the result that the magnetic properties of the core are not uniform and soft spots are formed by the accumulated filler. These soft spots are deficient in mechanical strength and usually produce cracks in the core during the pressing or assembly operations.

In accordance with one embodiment of the present invention, a core containing magnetic particles smaller than 400 mesh in size can be produced with a high degree of mechanical imam. (Cl. 175- 21) Thisinventlon relates't'o the manufacture of I magnetic cores-, andmore particularly to the; manufacture or insulated "dust type" magnetic cores in which small insulated particles or mag-1 netic material are compressed into a body, .An object oi this invention is the provision particles andiin th ahd a uniform effective' permeability rating accurately established, at predetermined values.

The small magnetic particles are first coatedwith a primary insulation-5i comprising a magnesium h rox sodium silicate and'talc. 'I'Ee coa e particles'a'ie then combined with dry lga lip and colloidal clay in an enclosed mixing apparatus an s rred for a definite period, after which a soiutipnpLspdium silicate and mflfl esiunrahydroxide in water is thereto. The resultant mass 'is stirred until it forms into small balls or spheres, which are heat treated, pulve riggd into remway coarse all? compressed into the core structure. The resultant core'is strong, free from cracks, and has uniform properties throughout, due to the distribution and treatment 0! the spacing agent in the core body.

, This procedure is suitable for making highquality cores from a variety of magnetic materials and can be adapted to the manufacture The lnvention is particularly adapted for use with of cores from various metals and alloys.

nickel-iron, alloys of the permalloy type and the following detailed description is directed primer-- ily to the production of cores from this type of alloy. A v

The magnetic particles used in these cores can be prepared by any suitable method. One process-for producing nickel-iron magnetic alloy particlesis fully described in Patent 1,669,649, issued May 15,1928 to C. P. Beath'and H. M. E.

Heinicke.

In manufacturing the particles into cores, the particles are initially provided with a primary insulating coating. This coating and its application is disclosed in my Patent No. 2.105.070,

.' which issued January 11, 1938. As stated in'that patent, this coating comprises magnesiumhydroxide (mil ligf magnesia), sodium silicate, and

talc and is preferably applied insete'rm layers. For the first layer a solution is made of water,

magnesium fiyi'iro'iide and sodium silicate. The magnetic particles are thoroughly mixed with this solution, after which the coated particles are heated to a temperature between 275 F. and 300 F. to evaporate the water and form an initial set in the insulating material so that it will not be redissolved in the application of subsequent coatings. The second layer is applied by immersing the particles In? similar solution to which talc has been added. The particles are then again heated and two additional layers may be applied in the same manner, making a total of four layers in all. The ingredient proportions aremodiiled for the. various coatings, as explained in the patent. and the amount of insulating material is adjusted in accordance with the fineness of the particles and resultant particle surface area to be covered. I i,

In the second process step the coated particles are dry mixed with a filler or particle spacing agent. As stated above man and colloidal clay are suitable for this purfiYsTa'nd amixtfiie containing about equal parts of the kaolin and colloidal clay gives excellent results. The quantity of mixture to be added depends upon the permeability desired in. the completed core and must be carefully measured. In general, the quantity of kaolin-gia may be equal to from 4% to 20% of the total weight of the coated magnetic particles, the core permeability being reduced as the quantity of filler is increased.

In the dry mixing operation, the particles, kaolin and colloidal clay are placed in a closed tumbling barrel of the usual type and tumbled until the materials are thoroughly oommingled. A tumblingperiod of about ten minutes, with the barrel closed, is usually adequate, but the operation should be continued until a portion of the kaolin-clay mixture is coated on the particles and the remainder is dispersed throughout the particle mass.

-In the third process step a solution is added to spacing agent. This solution is made by dissolving sodium ilieate animagnesium hydrg ide in distilled water, The exact quantity and proporons 0 ese ingredients will depend largely upon the nature and the quantity of particle spacing agent present. In making cores of 400 mesh dust containing a quantity of 50-50 kaolinclay equal to 4% of the dust weight, good results were obtained with the following solution:

i and combined with the mixtfi'lifparticles and Weight-Wet basisper cent of total particle weight Sodium silieafe ,75 Magnesium hydroxide 1.25 Distilled water 3.50

Total 5.50

In one type of core the filler weight is equal to 6% of the particle weight and the following solution is employed in that construction:

Weight-Wet basisper cent of total particle weight Sodium silicate 1.2 Magnesium hydroxide 2.0 Distilled water 3.5

Total 0.7

For cores made of 400 mesh dust and a 50-50 kaolin-clay filler equal to 20% of the total particle weight the following solution is employed:

The proper quantities of sodium silicate and magnesium hydroxide to be used with other pro- 40 portions of filler can be determined by interpolation of the ranges given in the above tables. The quantity of water remains constant and the other ingredient proportions are varied with the filler content. Thus, the solution weight will be I 5.5% of the particle weight when 4% filler is used;

and 13.5% of the particle weight when 20% filler is used.

The solution is poured over the dry mixture in the tumbling barrel and time is allowed for the solution to become absorbed. The barrel is then 5 rotated and the wet mass is worked with a scraping tool. [is the tumbling or mixing progresses, the wet mass formbodies or spheres of increasing size. After about ten minutes of tumbling, these spheres or balls attain a diameter 10 around one inch and they ar"e then removed from the barrel.

' In the next operation, the spheres are placed in a ventilated oven while wet and then heat treated therein. The spheres are first heated at a teml5 perature between F. and F. for about two hours and themfitfii'fii'ediate cooling, they are heated at a temperature of between F. and 19552. for an additional period of about two "h0l1l'S.I *-In one satisfactory process the 2 spheres are heated at around 150 F. for about two hours and then heated at around 186 F. for about two hours. At the end of this heat treatment the spheres aggmfl-Bihi fl and they can be stored, preferably in covered containers, in this 25 condition for an indefinite period.

In the next operation, the heat treated spheres are ground or pulverized by means of any suitable apparatus, into relatively coarse particles. The grinding is continued only until the particles 30 will pass through an 80 mesh screen and it is desirable for as many of the particles as possible to approximate this maximum size.

The coarse particles are next r essed into core bodies by the usual methods. ritfils'operation 35 the coarse particles are placed in a die cavity and then compressed by means of a member which is forced into the cavity. Very high pressures, around 250,000 pounds per square inch of forming member'surface, are employed to compress 40 the member into a unitary body of desired configuration.

With the above described process a high percentage of particle spacing agent can beinoorporated effectively in the core to provide wide 45 flexibility in adjustment of core permeability. The magnetic properties of the core are uniform because the spacing agent is dispersed uniformly throughout the core structure. All of the spacing agent can be incorporated eiilciently and ef- 50 fectively in the core and, consequently, the permeability values of the core can be controlled within narrow limits. 'The coarse particles produced from the spheres bond readily in the pressing operation and the resultant cores have high 5 mechanical strength to withstand the handling and stresses to which they are subsequently subiected. Because segregation of the spacing agent is prevented, the formation of soft spots and the tendency for the cores to crack is avoided.

Although the above description covers a speciflc embodiment of the invention that is adapted to one type of core structure, these procedures can be used in making cores of various magnetic metals and alloys and modifications of these methods are feasible. In place of the kaolin-colloidal clay combination other mate i .are c .2- j

terial should preferably have a similar particle size range. For the solution that is added to-the 75 particle-filler mixture it is possible to use otheg metallic hydrates such as hydrates of bismuth, aluminum, zinc and cadmium, in place of the magnesium"cTTFipoundT Kl's silicates, such as potassium silicate, can be substituted for the so um s ica e. 1 j I While the use of the specifically disclosed materlals is preferred, certain modifications can be made therein with satisfactory results, and it is until it forms into small bodies, heat treating said bodies, pulverizing the heat treated bodies into relatively coarse particles, and forming said particles into a core.

2. In a method of making a magnetic core, the steps of coating finely divided magnetic particles with insulation, dry mixing the coated particles with kaolin and colloidal clay, adding to the dry mixture a solution of a metallic hydroxide and an alkali metal silicate, mechanically mix-. ing the resultant mass until it forms in o small bodies, heat treating said bodies, pulverizing the heat treated bodies into relatively coarse particles, and compressing the coarse particles into a core.

3. In a method of making a magnetic core, the

steps or coating finely divided magnetic particles with insulation, dry mixing the coated particles with a chemically inert material for spacing the particles; adding to the dry mixture a solution of a metallic hydroxide and an alkali metal silicate, mechanically mixing the resultant mass until it forms into small bodies. heat treating said bodies, pulverizing the heat treated bodies into relatively coarse particles, and forming said coarse particles into a core.

4. In a method of making a magnetic core, the steps of coating finely divided magnetic particles with insulation, dry mixing the coated particles with a chemically inert material for separating the particles, adding to the dry mixture a solution comprising water, magnesium hydroxide and sodium silicate, mechanically mixing the resultant mass until it forms into small bodies, heat treating said bodies, pulverizing the heat treated bodies into relatively coarse particles, and forming the coarse particles into a core. 5. In a method of making a magnetic core, the steps of coating finely divided magnetic particles with insulation, dry mixing the coated particles with a chemically inert material for separating the particles, adding to the dry mixture a solution comprising water, magnesium hydroxide and sodium silicate,mechanicallymixing the resultant mass until it forms into small spheres, heating the spheres at a temperature between 140 and 160 F'.,,subse quently heating the spheres at a temperature between 175 F. and 195 F., pulverizing the heat treated spheres into relatively coarse particles, and compressing the coarse particles into a core.

6. In a method of making a magnetic core. the steps of coating finely divided magnetic particles with insulation, dry mixing the coated 1| particles with kaolin and colloidal clay, adding I Cross Reference A T a,as'o,2 2a

-cate, mechanically mixing the resultanto, other alkali metal a magnetic core,.

a a Diem to the dry mixture 2. solution comprising water, a metallic hydroxide and an alkali metal sili- I mass until it forms into small spheres, heating the .spheres at atemperature between 140 and 5 160 F. for about two hours, subsequently heating the spheres at a temperature between 1'75 F. and 195 F. for about two hours. pulverizing the heat treated spheres int'o relatively coarse particles, and compressing the coarse particles into a core. 7. In a math of making a magnetic core. the steps oi dry mixing finely divided and coated particles of magnetic material with kaolin and clay, the total weight of the kaolin and clay being equal to from 4% to of the weight cf the coated particles, adding to the commingled particles, clay and kaolin a solution comprising water, magnesium hydroxide and sodium silicate, the total weight of added solution being from 5.5% to 13.5% of the weight of the coated particles, mechanically mixing the combined particles with the agent and solution until the mass forms into small spheres, heat treating said spheres, pulverizing the heat treated spheres into relatively coarse particles, and compressing the coarse particles into a core.

8. In a method of making a magnetic core, the steps or dry mixing finely divided and coated particles of magnetic material with a material for separating the coated particles, said separating material comprising kaolinand colloidal clay in about equal proportions and the total weight 01 the material being from 4% to 20% of the weight of the coated particles, adding to the dry mixture a solution comprising water, magnesium hydroxide and sodium silicate, mechanically mixing the resultant mass until it forms into small spheres, heating said spheres at a temperature between 140 F. and 160 F., subsequently heating the spheres at a temperature between 175 F. and 195 F., pulverizing the heat treated spheres into relatively coarse particles, and compressing the coarse particles into a core.

9. In a method of making a magnetic core, the steps of dry mixing finely divided and coated particles 01' magnetic material with a material -!or separating the coated particles, said separating material comprising kaolin and colloidal clay in about equal proportions and the total weight 5 oi the material being from 4% to 20% of the weight of the coated particles, adding to the dry mixture a solution comprising water, magnesium hydroxide and sodium silicate, mechanically mixing the resultant mass until it forms into small spheres, heating said spheres at a temperature around 150 F. for about two hours, subsequently a heating the spheres at a; temperature around 186 I". for about two hours, pulverizing the heat treated spheres into relatively coarse particles, and compressing the coarse particles into a core. 10. In a method of making a magnetic core, the steps of dry mixing finely divided and coated particles of magnetic material with a material for separating the coated particles, said separating material comprising kaolin and colloidal clay in about equal proportions and the total weight of the material being from 4% to 20% oi. the weight oi the coated particles, adding to the dry mixture a solution comprising water, magnesium hydroxide and sodium silicate, the total weight of the solution being from 5.5% to 13.5% of the weight of the particles, mechanically mixing the resultant mass until it forms into small spheres, heating said spheres at a temperature between 195 F., pulverizing the heat treated spheres into relatively coarse particles, and compressing the.

coarse particles intoacore. 1

11. In a method 01 making a magnetic core, the steps of dry mixing finely divided and coated particles of magnetic material with a. material for separating the coated particles, said separat-.

ing material comprising kaolin and colloidal clay in about equal proportions and the total weight of the material being about. 4% of the weight of the coated particles, adding to the dry mixture a solution comprising. water, magnesium hydroxide. and sodium silicate, the weight of said solution being about 5.5% of the weight oi the particles,-

mechanically mixing the resultant mass until it forms into small spheres, heating said spheres at a temperature between 140 F. and 160 F., subsequently heating the spheres between a tem perature of 175 F. and 195' I"., pulv'erizing the heat treated spheres into relatively coarse particles, and compressing the coarse particles .into

a core. a.

12. In a method oimaking a magnetic core, the steps of dry mixing finely divided andcoated particles of 'magnetic material with an agent for.v

separating the particles, said separating agent comprising dry kaolin and colloidal clay in about equal proportions and the total weight of thejf agent being from 4% to of the weight'oi the coated particles, adding to the dry-mixture a solution comprising a quantity-oi water equal to 3.5% of the particle weight, aquantity oi" magnesium hydroxide equal to from 1.25% to 6.30% of the particle weight, and sodium silicateequal to from 375% to 3.70% of the particle f weight, mechanically mixing the resultant mass until it forms into spheres around one inch in diameter, heating said spheres, pulverizing the heat treated spheres into relatively coarse particles, and compressing said relatively coarse partlcles into a core. l

13. In a method of making a magnetic core, the steps of dry mixing finely divided and coated particles or magnetic material with an agentior v coarse particles into a core.

g v a,'so,2aa F. and F., subsequently heating the spheres between a temperature of F. and,

lution comprising a quantity or water equal to 3.5% o! the particle weight, a quantity of magnesium hydroxide 'equal to 2% o! the particle weight, and sodium silicate equal to -1.2% oi. the particle weight, mechanically mixing the resultant mass until it terms into spheres around one inch in diameter, heating said spheres at a, temperature betweenjlii), I". and 160]? for two hours, subsequently [heating said spheres at a temperature between 175 F. and F., pulverizing the heat treated spheres into relatively coarse particles,-and compressing said relatively 14. In a method of making amagnetic core, the steps 0! coating finely divided particles of a nickel-iron magnetic alloy with a mixture of H magnesium hydroxide, sodium silicateand talc,

separating the particles, said separating agent. comprising drykaolin and colloidal clay in about I equal proportions and the total weight of the agent being equal to about 6% of the weight of the coated particles, .dry mixing the'particles and agent until a portion of the, agentis'coated on p l 30 the. particles and the remainder isg;-disp ersed through the' particle mass, adding to the dry mixture a solution comprising a quantityjoi water equalt'o 3.5% of the'parti'cle weight, a quantity I of magnesium hydroxide equal to 2% of the particle weight, and a quantity oi sodium silicate equal to 1.2% of the particle weight, mechanicallymixingflthe resultant mass until 'itiorrns "combining the coated particles with an agent for r I into spheres around one inch in diameter, heating said spheres at a temperature around 150? F. for about two hours, subsequently heating the spheres atv a temperature around 186 I. for

about two hours.fpulverizing the heat treated relatively coarse particles into \a core.v

- spheres into relatively coarse particles, and compressing said 

